1. Field of the Invention
The present invention relates to an antenna device and a communication terminal device preferably for use in a communication system of an HF band or a UHF band.
2. Description of the Related Art
As a system for performing charging or article management, an RFID (Radio Frequency Identification) system has prevailed. In the RFID system, a reader/writer and an RFID tag are caused to wirelessly communicate with each other using a non-contact method, and high-frequency signals are transmitted and received between these devices. Each of the reader/writer and the RFID tag includes a wireless IC chip used for processing the high-frequency signal, and an antenna element used for transmitting and receiving the high-frequency signals. For example, in a HF-band RFID system utilizing a 13.56 MHz band, as the antenna element, a coiled antenna is used, and an antenna coil on a reader/writer side and an antenna coil on a tag side are coupled to each other through an induction magnetic field.
In this HF-band RFID system, for example, in a such a way as a FeliCa (registered trademark) compatible terminal illustrated in Japanese Patent No. 4325621, an antenna coil is embedded in a portable communication terminal and the communication terminal itself is used as a reader/writer or an RFID tag, in some cases. FIG. 15 is the longitudinal cross-sectional view of a contactless IC card reader/writer 1 described in Japanese Patent No. 4325621.
The contactless IC card reader/writer 1 includes an antenna substrate in which a loop antenna and a capacitor are provided in the top surface thereof, a control substrate 6 in which a transmission and reception circuit and a chip-type coil 5 are provided in the top surface thereof, a magnetic sheet 10 disposed between an antenna substrate 4 and the control substrate 6, and an insulating case 15. In order to form an aperture portion 11 above the chip-type coil 5 provided in the control substrate 6, the magnetic sheet 10 is disposed so as to avoid the upper side of the chip-type coil 5. As illustrated by a magnetic flux φ1, the chip-type coil (feed coil) 5 is coupled to the loop antenna in the antenna substrate 4 through an induction magnetic field. As illustrated by a magnetic flux φ2, the antenna substrate 4 is magnetic-field-coupled to an IC card 20. With this structure, without using a contact pin or a flexible cable, it is possible to substantially connect an RFID IC chip and an antenna coil to each other.
However, in recent years, with the functional enhancement and the miniaturization of communication terminals, it has become difficult to secure, within a terminal chassis, a sufficient space for disposing an antenna coil, a wireless IC chip, and a feed coil. For example, even though an antenna coil is disposed on one main surface side of a printed wiring substrate, there is not a space on this main surface side in some cases, the space being used for disposing the wireless IC chip and the feed coil. In this case, it is necessary to provide the wireless IC chip on the other main surface side of the printed wiring substrate and connect this wireless IC chip to the antenna coil provided on the one main surface side of the printed wiring substrate through a flexible cable or the like.